00'Runner

Found a puddle of oil under the 4Runner this morning. Climbed under and see that it's coming from around the t-case. Not being super mechanical, visions of dollar signs flying from my wallet are bountiful! I was hoping to at least know a little bit of what could be wrong before taking it in for and getting robbed at the mechanic!

I took a quick picture and was hoping that someone could tell me what the silver part is where the oil leak is coming from. The leak is coming from where the green arrow is and the red arrow is pointing at the part I'm not sure the name of.

Thanks for any help!!!